Several variants of syringes of this kind are known to the art.
In a first variant of these known syringes the mutual co-action of the plunger and the rod-shaped element is facilitated with the aid of means located between said plunger and said element, this means holding the plunger to the rod-shaped element during linear movement of the element in said first direction and also during linear movement of the element in said second direction. Thus, there is no detachable connection between the plunger and the rod-like element and the plunger will thus be moved backwards and forwards in the container in precise response to the direction of movement of the rod-shaped element.
This means that the container can be filled with liquid each time the plunger is moved away from the needle, and emptied of liquid each time the plunger is moved towards the needle, thereby enabling the syringe to be used over and over again.
The repeated use of one and the same syringe has proven to constitute a serious risk of spreading disease, such as AIDS.
Consequently, single-shot syringes have been proposed, which can be used only once for injection purposes, after which the container can no longer be filled.
An example of such single-shot syringes is described and illustrated in European Patent Application Ser. No. 0 229 017, in which syringe the plunger and rod-shaped element co-act with one another through the intermediary of hook-shaped members which are moved out of engagement with the plunger upon movement of the rod-shaped element towards the needle.
The Swedish Patent Specification Publ. No. 413 838 describes and illustrates a so-called single-shot syringe in which the rod-shaped element incorporates a weakening at a location adjacent the plunger, and in which means are provided for twisting the element relative the plunger subsequent to completing an injection, thereby fracturing the rod-shaped element at the weakened location.
The Swedish Patent Specification Publ. No. 438 598 also teaches a single-shot, or disposable, syringe.